Up to now, fetal movement frequency detecting methods and detecting devices are known which detect the number of fetal movements perceived by a pregnant woman in a fixed period of time in order to grasp whether a fetus is growing smoothly in a uterus.
As such fetal movement frequency detecting methods and devices, various kinds of methods and devices have been proposed and implemented which are configured so that a pregnant woman pushes a button when feeling a fetal movement or so that a fetal movement sensor for detecting fetal movements is attached on a pregnant woman's abdomen in order to determine whether there is a fetal movement on the basis of an output signal from the fetal movement sensor.
For example, a technique disclosed in Japanese Unexamined Patent Publication No. 11-89832 (Patent Document 1), detects fetal movements using a thin-film piezoelectric sensor, and determines that the fetus is healthy if a predetermined number 10 or more of fetal movements are detected within a fixed period of time (two hours). A technique is disclosed about a fetal movement measuring instrument which determines that the fetus is in a dangerous condition if the number of fetal movements in a fixed period of time (8 hours) is less than a predetermined number 10.
However, there are differences among fetuses and among the numbers of fetal movements caused when a fetus moves actively, rests, and so on by time period, so that it is difficult to determine whether the fetus is growing healthy or not from the number of fetal movements. In addition, there are various types of fetal movement including those occurring for a few minutes at intervals of two or three seconds such as “hiccups” and those occurring singly such as “kicks” and “rolls”. When such types of fetal movement are taken into consideration, it is extremely difficult to predict or determine well-being of a fetus only by detecting a fetal movement frequency as described above.
Furthermore, no movement of a fetus in a fixed period of time cannot necessarily decide that the fetus is in a dangerous condition. For example, the tendency has been confirmed that a change in fetal movement of a healthy pregnant woman gradually becomes remarkable and the number of occurrences of it increases from 20 weeks of gestation. In addition, the tendency has been confirmed that at a time of delivery a fetus in a uterus moves downward and thereby fetal movements cannot be detected appropriately by a normal fetal movement sensor resulting in a small change in fetal movement and a reduced frequency of it.
In addition, high sensitivity employed for detecting fetal movements in a uterus by signals from a pregnant woman's abdomen catches a signal from the woman by her movement such as respiration and heart beats to count as one component of fetal movement, thereby shows a number beyond actual fetal movements, resulting in a risk of missing that the fetus has a reduction in fetal movement.
Furthermore, in Japanese Unexamined Patent Publication No. 10-511015 (Patent Document 2), a fetus monitoring device is disclosed which is configured so as to receive an electric signal representing an activity of a fetus from a sensor which is a pressure or acceleration detector using a piezoelectric film and is attached to a pregnant woman's abdomen, compare the electric signal with predetermined signal series by a comparator, and produce an output representing activity of the fetus. A device and a method for monitoring a fetus configured like this are assumed to serve to provide objective data of growth of a fetus to an obstetrician or the like to detect a disease or abnormality of the fetus.
The proposed fetus monitoring device detects, with a sensor, small movements caused by heart beats, breathing movements, and movements of the body of a fetus, converts these movements to electric signals, and identifies the movements by the frequency components of them. Furthermore, it has also been proposed that two or more sensors are used to clearly distinguish signals indicative of fetus movements and thereby signals caused by various physiological movements of a pregnant woman such as physical movements, respiration, and heart beats of the pregnant woman are simultaneously recorded.
In this proposal, the sensitivity of the sensor is likely to be raised to record movements of a fetus, heart beats, and breathing movements of the fetus, and for this reason, respiration and heart beats of the pregnant woman are detected as signals, so that signals of the pregnant woman are mixed with signals from the fetus resulting a difficult distinction between both. According to FIG. 7, the problem that the heart rate of a fetus becomes 300 times or more for one minute occurs. In other words, in this case, signals including those of the pregnant woman are shown and movements of the fetus are not recorded accurately. Moreover, it is shown that respiration movements of the pregnant woman are picked up very easily when a piezoelectric film is used as the sensor.
Furthermore, in this proposal, how to deal with individual differences among fetuses and fetal movements including, as described above, those occurring two or more times at a constant cycle such as “hiccups”, those occurring singly such as “kicks” and “rolls”, and the like is not disclosed at all. It is difficult to determine concrete fetal movements from analysis of frequency components, and is not sufficient to predict or determine well-being of a fetus.
Furthermore, it is assumed that the predetermined comparator includes the heart rate, breathing movements, and physical movements of a fetus, but growing processes of the fetus by weeks from the conception are not almost considered, so that it is impossible to compare these signals. Thus, the proposed device is not able to determine that a fetus is in a dangerous condition. In other words, as described above, at least the following tendencies are observed in fetal movements of a healthy pregnant woman. (1) The tendency has been confirmed that a change in fetal movement gradually becomes remarkable and the number of occurrences of fetal movement increases from the 20 weeks of gestation. (2) The tendency has been confirmed that at a time of delivery a fetus in a uterus moves downward and thereby fetal movements cannot be detected appropriately by a normal fetal movement sensor resulting in a small change in fetal movement and a reduced frequency of it. Processing by a simple comparator based on the same criteria of determination without consideration of these tendencies of fetal movement in different periods of time means that information processing related to fetal movements corresponding to stages of growth of a fetus is performed, and its problem awareness is not shown at all. Thus, it is difficult to appropriately predict or determine well-being of a fetus by the proposed device or method.    Patent Document 1: Japanese Unexamined Patent Publication (Kokai-Koho) No. 11-89832    Patent Document 2: Japanese Unexamined Patent Publication (Kohyo-Koho) No. 10-511015    Non-patent Document 1: Eugenius S. B. C. Ang, Jr. et al., “Prenatal exposure to ultrasound waves impacts neuronal migration in mice”, PNAS, Aug. 22, 2006, vol. 103, No. 34, 12903-12910